Java 17 Recipes

8-8. Iterating Over Files in a Directory
 Problem
You need to scan files from a directory. There are possibly subdirectories with more files. 
You want to include those in your scan.
 Solution
Using the NIO.2, creates a 
java.nio.file
.FileVisitor interface object and performs 
the desired implementation within its visitFile method. Next, obtain the default 
FileSystem object and grab a reference to the path you’d like to scan via the getPath() 
method. Lastly, invoke the Files.walkFileTree() method, passing the Path and the 
FileVisitor that you created. The following code demonstrates how to perform 
these tasks.
public class Ch_8_8_TraverseDirectory {
private void start() {
FileVisitor
myFileVisitor = new SimpleFileVisitor
() {
@Override
public FileVisitResult visitFile(Path file, 
BasicFileAttributes attrs)
throws IOException {
System.out.println("Visited File: "+file.toString());
return FileVisitResult.CONTINUE;
}
};
FileSystem fileSystem = FileSystems.getDefault();
Path directory= fileSystem.getPath(".");
try {
Files.walkFileTree(directory, myFileVisitor);
} catch (IOException e) {
e.printStackTrace();
}
}
ChApTer 8 InpuT And OuTpuT

---

316
public static void main (String args[]) {
Ch_8_8_TraverseDirectory traverseDirectory = new Ch_8_8_
TraverseDirectory();
traverseDirectory.start();
}
 How It Works
Before NIO.2, trying to traverse a directory tree involved recursion, and depending on 
the implementation, it could be very brittle. The calls to get files within a folder were 
synchronous. They required scanning the whole directory before returning, generating 
what would appear to be an unresponsive method call to an application user. With 
NIO.2, one can specify which folder to start traversing on, and the NIO.2 calls handle the 
recursion details. The only item you provide to the NIO.2 API is a class that tells it what to 
do when a file/folder is found (
java.nio.file
.SimpleFileVisitor class implementation). 
NIO.2 uses a Visitor pattern, so it isn’t required to prescan the entire folder but instead 
processes files as they are being iterated over.
The implementation of the SimpleFileVisitor class as an anonymous inner 
class includes overriding the visitFile(Path file, BasicFileAttributesattrs() 
method. When you override this method, you can specify the tasks to perform when a 
file is encountered.
The visitFile method returns a FileVisitReturn enum. This enum then tells the 
FileVisitor which action to take.
• CONTINUE continues with the traversing of the directory tree.
• TERMINATE stops the traversing.
• SKIP_SUBTREE stops going deeper from the current tree level (useful 
only if this enum is returned on the preVisitDirectory() method).
• SKIP_SIBLINGS skips the other directories at the same tree level as 
the current.
The SimpleFileVisitor class, aside from the visitFile() method, also contains 
the following.
• preVisitDirectory is called before entering a directory to be traversed.
• postVisitDirectory is called after finished traversing a directory.
ChApTer 8 InpuT And OuTpuT

---

317
• visitFile is called as it visits the file, as in the example code.
• visitFileFailed is called if the file cannot be visited; for example, 
on an I/O error.